In the course of a flight, situations arise where the pilot must request clearances or deviations in the flight plan due to weather, aircraft performance, or fuel constraint through Controller Pilot Data Link Communications (CPDLC). A flight plan generally includes basic information such as, but not limited to, departure and arrival points, estimated time en route, alternate airports, number of people on board, endurance and information about the aircraft itself. In general, different types of requests will be made to Air Traffic Control (ATC) through a CPDLC data link for clearances or deviations. These can include vertical clearances, crossing constraints, route deviation, and speed changes.
While performing CPDLC downlink requests, due to pilot resource limitations, the pilot is not always aware of the optimal deviation for the flight plan course and must depend on the Flight Management System (FMS). To do this, the pilot manually looks into the FMS and enters the FMS computed data manually in Communication Management Unit (CMU) pages or Communication Management Function (CMF) pages for ATC downlink requests and reports.